Polycarbonates each have excellent characteristics, such as transparency, heat resistance, and mechanical characteristics, and hence have been used in a wide variety of applications including: casings for OA equipment and a household electric appliance; parts in electrical and electronic fields; and optical materials, such as a lens. Many of the polycarbonates used in the wide variety of applications are each a linear polymer obtained by causing a dihydric phenol and a carbonate precursor, such as phosgene, to react with each other. However, the polymer shows Newtonian flow behavior under a melt processing condition, and hence when blow molding, extrusion molding, or foam molding is performed, drawdown is liable to occur owing to its self-weight. The drawdown causes a problem particularly in the case of large-scale molding.
In order to alleviate such problem, a branched polycarbonate that shows non-Newtonian flowability under a melt processing condition and hence hardly causes drawdown at the time of its melting has been preferably adopted in the above-mentioned molding applications.
The production of the branched polycarbonate through the use of an interfacial polymerization method or an ester exchange method has been known as a method of producing the polycarbonate. When the branched polycarbonate is produced by using the ester exchange method, raw material components are melted under high temperature and subjected to an ester exchange reaction for polymerization. The branched polycarbonate to be obtained is liable to color owing to, for example, an influence by a polymerization catalyst to be used in the reaction. Therefore, it is not preferred to produce the branched polycarbonate through the use of the ester exchange method in an application where transparency is required.
As a method of producing the branched polycarbonate through the use of the interfacial polymerization method, in Patent Document 1, there is a disclosure of two production methods, i.e., a method involving using a polycarbonate oligomer into which a branching agent has been incorporated, and causing the polycarbonate oligomer and a dihydric phenol to react with each other to provide the branched polycarbonate, and a method involving using a polycarbonate oligomer into which no branching agent has been incorporated, and causing the polycarbonate oligomer, and a branching agent and a dihydric phenol to react with one another to provide the branched polycarbonate.
In the former method involving using the polycarbonate oligomer into which the branching agent has been incorporated, and causing the polycarbonate oligomer and the dihydric phenol to react with each other to provide the branched polycarbonate, a unit derived from the branching agent in the branched polycarbonate becomes more uniform as compared to the latter method involving using the polycarbonate oligomer into which no branching agent has been incorporated, and causing the polycarbonate oligomer, and the branching agent and the dihydric phenol to react with one another to provide the branched polycarbonate, and hence physical properties become more uniform than those in the latter production method. Accordingly, the former method is a preferred method.
However, the method involving using the polycarbonate oligomer, into which the branching agent has been incorporated, and causing the polycarbonate oligomer and the dihydric phenol to react with each other to provide the branched polycarbonate involves the following problem. When the polycarbonate oligomer into which the branching agent has been incorporated is continuously produced, an intermediate phase occurs at the time of the separation of a reaction liquid containing the polycarbonate oligomer into which the branching agent has been incorporated into an organic solvent phase containing the polycarbonate oligomer and an aqueous phase to deteriorate separability, and hence production efficiency remarkably reduces.